1. Field of the Invention
This invention relates to a starter motor, and more particularly to a starter motor having an oil seal which slidably contacts with a pinion moving member.
2. Description of the Prior Art
FIG. 18 is a sectional view showing part of an exemplary one of conventional starter motors. Referring to FIG. 18, the starter motor shown includes an output rotary shaft 1 connected to an armature rotary shaft 3 of the motor by way of an epicycle reduction bear 2. A helical spline 1a is formed on an outer periphery of the output rotary shaft 1, and an overrunning clutch 4 is spline fitted on the helical spline 1a. A pinion driving shaft 5 is formed in an integrated relationship with an inner member of the overrunning clutch 4 and mounted for axial sliding movement and for integral rotation on the output rotary shaft 1, and a pinion 6 is formed at an end of the pinion driving shaft 5, thereby forming a pinion moving member. A ball bearing 7 with a seal is fitted in a front bracket 8 which makes part of a machine frame of the starter motor. The ball bearing 7 receives an outer periphery of the pinion driving shaft 5 for axial sliding movement and for rotation relative to the front bracket 8. The front bracket 8 has a front end portion which extends forwardly in a tubular configuration such that it covers over an outer periphery of the pinion 6. An oil seal 9 made of rubber is disposed at a location in the front bracket 8 on the front side of the ball bearing 7 such that it slidably contacts at a lip face at an inner circumferential end edge thereof with an outer peripheral face of the pinion driving shaft 5. The oil seal 9 is constituted such that, as shown more particularly in FIG. 19, it is fixed at an outer circumferential fixing portion 9a thereof to the front bracket 8 and a rear wall 9b extends inwardly from a rear end of the outer circumferential fixing portion 9a, and a contacting portion 9c extends obliquely forwardly from a radially inner end of the rear wall 9b and terminates in the lip face. Thus, the oil seal 9 has a cross section having a forwardly open channel shape as seen in FIG. 19.
A sleeve bearing 10 is disposed on an inner periphery of the pinion driving shaft 5 for supporting the output rotary shaft 1 thereon. The output rotary shaft 1 has a stopper 11 mounted at a front end portion thereof for abutting with a shoulder 5a of the pinion driving shaft 5 to stop axial movement of the pinion driving shaft 5 in the forward direction. Further, a cap 12 having a channel-shaped cross section is mounted in an inner periphery of a forward end portion of the pinion 6 such that it covers an opening at the front end of the pinion 6.
The starter motor further includes an electromagnetic actuator 13 in the form of a solenoid, and a lever 14 mounted for pivotal motion and having one end held in engagement with a plunger 15 of the electromagnetic actuator 13 and the other end held in engagement with a rear side of the overrunning clutch 4.
In operation, when the electromagnetic actuator 13 is energized, the plunger 15 is attracted to pivot the lever 14 to move the overrunning clutch 4 forwardly. Consequently, the pinion driving shaft 5 is moved axially forwardly to move the pinion 6 into meshing engagement with a ring gear of an internal combustion engine not shown. Meanwhile, as a result of such energization of the electromagnetic actuator 13, the motor is energized to start its rotation, and rotation of the armature rotary shaft 3 is transmitted to the output rotary shaft 1 by way of the epicycle reduction bear 2 and further to the pinion driving shaft 5 by way of the overrunning clutch 4 so that the pinion 6 is rotated and the engine is started by way of the pinion 6. After starting of the engine, the electromagnetic actuator 13 is deenergized, and the pinion 6 is returned to its original position by a return spring not shown disposed suitably in the front bracket 8.
In the conventional starter motor having such a construction as described above, the oil seal 9 is provided for waterproof and dust-proof features for sliding contact portions of the ball bearing 7 and the pinion driving shaft 5 and for the inside of the front bracket 8. Since the oil seal 9 has such an inwardly concave channel-shaped section as described above, water which may be admitted from the front side is likely to accumulate in a spacing 9d defined by the oil seal 9 and the front bracket 8. Besides, since another spacing is defined between a front end portion 8a of the front bracket 8 and the pinion 6, water is likely to accumulate also in the spacing. In case heat is applied, in addition to vibrations or fine motion of the pinion 6, to such accumulated water, then the water may be admitted into the inside of the motor and cause various problems that internal parts of the motor may suffer from rust, that the sliding contact portion of the pinion driving shaft 5 may suffer from rust to cause insufficient sliding movement thereof, that the inside mechanism of the starter motor may be wet with water and suffer from insufficient operation of the motor, and so forth. Those problems are particularly remarkable where the pinion 6 of the starter motor is mounted in a vertically upward orientation or in an upwardly inclined orientation.